The present invention relates to an electric transformer having an improved cooling system.
It is widely known in the art the use of electric induction devices, such as reactors or transformers, which exploit the electromagnetic induction for properly transmitting and distributing electricity over power lines.
In particular, the basic task of a power transformer is to allow exchanging electric energy between two or more electric systems of usually different voltages.
Most common power transformers generally comprise a magnetic core composed of one or more legs or limbs connected by yokes which together form one or more core windows; for each phase, around the legs there is arranged a coil which comprises a number of windings, usually indicated as low-voltage windings and high-voltage windings, or primary windings and secondary windings. It is also possible to have control or regulation windings.
The phase windings are realized by winding suitable conductors, for example wires, or cables, or strips, so as to achieve the desired number of turns; typical constructive configurations are for example the so-called multilayer or disc configurations, wherein the conductors are wound around a cylindrical tube which represents an optimal configuration as regard to filling the area available with useful material and providing also the maximum short circuit strength.
In particular, in the multi-layer winding technique, the conductor turns required for a coil are for example wound in one or more concentric conductor layers connected in series, with the turns of each conductor layer being wound side by side along the axial length of the coil until the conductor layer is full. A layer of insulation material is disposed between each pair of conductor layers. Axially-extending cooling ducts may also be formed between pairs of conductor layers. In U.S. Pat. No. 7,023,312, pre-formed cooling ducts are inserted between conductor layers during the winding of a coil.
In the disc winding technique, the conductor turns required for a coil are for instance wound in a plurality of discs serially disposed along the axial length of the coil; in each disc, the turns are wound in a radial direction, one on top of the other, i.e., one turn per layer. The discs are usually connected in a series circuit relation and are typically wound alternately from inside to outside and from outside to inside so that the discs can be formed from the same conductor. An example of such alternate winding is shown in U.S. Pat. No. 5,167,063.
Due to the intrinsic structural characteristics and functioning of these devices, the various components of the transformers, and in particular the active electromagnetic parts such as the windings, are subject to overheating; hence, a very important aspect for ensuring the proper functioning of transformers concerns the systems adopted for cooling the active electromagnetic parts of the transformers, and in particular the phase windings. Indeed, an excess of temperature may damage the windings, and in particular the insulating elements thereof, thus resulting in mechanical/electrical losses and adversely affecting the overall performances of the transformer.
To this end, at the present state of the known art and according to a widely used solution, the magnetic core and the various coils are immersed into a cooling fluid, typically a mineral oil, which is contained inside a transformer tank. One or more external radiators are provided at one or more sides of the transformer tank; due to natural convection, the cooling fluid flows into the radiators, exchanges heat with open air and then returns inside the tank at a lowered temperature. Sometimes, the circulation of the cooling fluid inside the tank is facilitated by using a pump.
Although this cooling solution works properly, it would be desirable to provide an electric transformer which has a further improved cooling system. The present invention is directed to such a transformer.